1. Field of the Invention
The present invention relates to a seat such as a vehicle seat for a seat occupant thereon.
2. Description of the Related Art
For example, a seat to be mounted on a vehicle is preferred to provide the so-called riding comfort by reducing shakes and quivers of a passenger during the running of the vehicle to reduce the load on the driving operation and by absorbing the vibrations during the running of the vehicle to reduce the physical load on the passenger. Not limiting to the vehicular seat, various seats are desired to reduce muscle fatigue even after prolonged periods of sitting additionally to improve the seating comfort.
Generally, a condition required for a comfortable seat is thought to include a mechanism having a lumbar support, a shoulder support, a head-rest or the like for holding to maintain a natural S-shape of a spinal column of the seat occupant.
As a mechanism for forming the S-shape of spinal column, a lumbar adjusting mechanism known as the Schukra backrest has been used. In such a mechanism, an air bag containing a changeable amount of air is for pressing the lumbar vertebrae and the shape of the lumbar portion supporting from the lumbar vertebrae to the central spinal area is adjustable by combining plate springs and links.
Here, the lumbar adjusting mechanism for the backrest is effective for holding the driving position and reduces the load on the seated comfort and the driving operation. Moreover, the lumbar support is enabled to mitigate the tension in the muscles by dispersing the supporting load of the lumbar. Further by changing a lumbar depth on the progress of time, the lumbar support is capable to mitigate the muscle stress.
However, the supporting load of the backrest distributes mainly along an area facing the spinal area, and the supporting load of the portion from the buttocks to the lumbar occupies about 30% of that of the entire backrest. Thus, the back and the lumbar portion are held on the backrest. The seating for a period longer than two hours disturbs the blood circulation to weaken the muscles and to generate a pain substance thereby to cause the lumbago.
In the seat of the prior art, moreover, the cushion and the backrest are separated enough to form a gap between the lower buttocks and the seat. This gap lowers the supporting power of the seat abutting the lumbar. When the upper body is rocked by the disturbances of the road surface while travelling, the supporting power of the seat become insufficient is compensated by the muscle strength of the lumbus.
Therefore, the seat may cause the muscle fatigue after long periods of sitting even achieving the seating comfort.